1. Field of the Invention
THIS INVENTION concerns a method of and apparatus for detecting and evaluating the electro-chemical characteristics of an object under test, and is particularly though not exclusively, concerned with the measurement of the electrical service capacity of in-circuit sealed electro-chemical cells and monoblocs.
1. Description of Related Art
The invention is especially concerned with the testing of battery systems of the type used to provide uninterruptible back-up power supplies in large installations such as computers, life support machines and radar controlled safety systems for air transport. Such back-up batteries are required so that if the mains supply should fail, they must provide electrical supply to their critical loads instantaneously or at least in no more than a millisecond or two.
Such batteries may be composed of several hundred cells with a design life of up to 12 years and costing perhaps several hundreds of thousands of pounds.
In-situ testing of such batteries is an essential requirement since such cells are connected in series or series-parallel, and if only one cell of a standard battery becomes faulty the entire back-up supply may be lost.
The failure of such battery systems is quite common causing considerable damage to the critical loads which they supply.
Managerial personnel of large computer centres, air traffic control systems, etc. which depend upon such back-up power supplies generally will not allow their critical loads to be used to test the system and so, conventionally, all such tests carried out on standby battery supplies involve the temporary shutting down of dependent systems in order to avoid consequent damage should the mains supply fail during the test. Upon shut-down the entire back-up battery is disconnected from the installation and connected to a large DC load bank and then submitted to a standard discharge test lasting up to three hours. Such tests are normally carried cut once or twice per annum and this typically can necessitate the critical load being off-line for up to three days. In addition, conventional testing typically consumes many hundreds of kilowatts of power, the energy being, “burnt off” as heat which results in considerably waste of time and energy resource.
A principal object of the present invention is to provide a portable instrument capable of testing individual cells or monoblocs in-situ, i.e. without disconnection of the back-up supply and without endangering the dependent system should the mains supply fail during the test.
The system should enable discharge testing of a single cell in a battery of multiple cells, while the cell is still in circuit and with no disruption to the on-line system. Preferably, after testing an entire battery and finding it to be, as a whole, in good condition a tertiary element of the system will enable sample discharge tests to be conducted on a small number of cells so that the whole battery condition can be extrapolated, obviating the necessity for an annual discharge test and showing notable savings to the end user in terms of down time, manpower and energy expenditure. The ability of an instrument to identify deterioration in a single cell, in batteries of many hundreds of cells, will enable an engineer to target and replace only weak or failing cells thus greatly extending the working life of the entire battery, saving not only on costs and manpower but also energy consumption.